Spinal implants configured for tissue sparing angle of insertion and related methods

ABSTRACT

Spinal implants that are configured for a minimally invasive approach to a patient&#39;s intervertebral disc space, optimized to avoid blood vessels and nervous tissue, maximizing endplate coverage and promoting sagittal balance, are provided. Insertion and fixation can be accomplished through a narrow access window, thereby allowing better access to more spinal levels while being less invasive than other approaches. The spinal implants may facilitate fusion, and include visualization features to assist in the implantation and verify proper placement and vary segmental angle of lordosis. Methods of implanting the spinal implants to treat a patient&#39;s spine are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application No.62/145,161, filed on Apr. 9, 2015, and entitled “SPINAL IMPLANTCONFIGURED FOR OBLIQUE ANGLE INSERTION AND RELATED METHODS,” the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to orthopedic implants, and moreparticularly, to minimally invasive spinal implants that facilitatefusion of bone segments and associated methods. Even more particularly,the disclosure relates to spinal fusion implants configured forinsertion along an oblique angular trajectory into the lumbar spine, andrelated methods.

BACKGROUND

The integrity of the spine and its subcomponents like the vertebralbodies and intervertebral discs, both of which are well known structuralbody parts that make up the spine, is a key factor to maintaining apatient's good health. These parts may become weakened, damaged orbroken as a result of trauma, injury, or disease (e.g., by tumor,autoimmune disease), or as a result of wear over time, or degenerationcaused by the normal aging process.

In many instances, one or more damaged structural body parts can berepaired or replaced with a prosthesis or implant. For example, specificto the spine, one known method of repair is to remove the damagedvertebra (in whole or in part) and/or the damaged disc (in whole or inpart) and replace it with an implant or prosthesis. In some cases, it isnecessary to stabilize a weakened or damaged spinal region by reducingor inhibiting mobility in the area to avoid further progression of thedamage and/or to reduce or alleviate pain caused by the damage orinjury. In other cases, it is desirable to join together the damagedvertebrae and/or induce healing of the vertebrae. Accordingly, animplant or prosthesis for rigid fixation of the vertebrae may beutilized to facilitate fusion between two adjacent vertebrae. Theimplant or prosthesis may be implanted without attachment means, orfastened in position between adjacent structural body parts (e.g.,adjacent vertebral bodies).

Typically, an implant or prosthesis is secured directly to a bonestructure by mechanical or biological means. One manner of spine repairinvolves attaching a fusion implant or prosthesis to adjacent vertebralbodies using a fixation element, such as a bone screw. Most implants andtheir attachment means are configured to provide an immediate, rigidfixation of the implant to the implantation site. Unfortunately, afterimplantation the implants tend to subside, or settle, into thesurrounding environment as the patient's weight is exerted upon theimplant. In some cases, this subsidence may cause the rigidly fixedattachment means to either loosen, dislodge or potentially damage one ormore of the vertebral bodies.

Several known surgical techniques can be used to implant a spinalprosthesis. The suitability of any particular technique may depend uponthe amount of surgical access available at the implant site. Forinstance, a surgeon may elect a particular entry pathway depending onthe size of the patient or the condition of the patient's spine, such aswhere a tumor, scar tissue, great vessels, or other obstacle is present.Other times, it may be desirable to minimize intrusion into thepatient's musculature and associated ligamentous tissue. In somepatients who have had prior surgeries, implants or fixation elements mayhave already been inserted into the patient's spine, and as such, animplant introduction pathway may have to account for these priorexisting conditions.

Thus, it is desirable to provide an implant that can be easily insertedusing minimally invasive retractor instrumentation in accordance with aspecific pathway or approach. This facilitates a segmental or openapproach to multiple levels of the spine. For example, in certainsituations, it is desirable to provide a spinal implant that can beinserted at an oblique angle into the lumbar spine to avoid damage tothe patient, while also being suitable for insertion by way of aminimally invasive approach.

BRIEF SUMMARY

The embodiments provide spinal implants that are configured for a tissuesparing or an oblique angular approach to a patient's intervertebraldisc space. The spinal implants may facilitate fusion, and includeanti-migration and anti-rotation features as well as visualizationfeatures to assist in the implantation and verify proper placement. Theimplants support a narrow access oblique surgical approach whilemaximizing endplate coverage and promoting sagittal balance. The obliqueapproach provides better access to more spinal levels and is potentiallyless invasive than other approaches including midline and lateralapproaches.

In accordance with one exemplary embodiment, a spinal implant isprovided having a body with an upper surface, a lower surface, and apair of sidewalls extending therebetween. The sidewalls may be connectedby an intermediate wall segment and converge at a nose or tip. The pairof sidewalls includes one sidewall that is longer than the othersidewall. The body may further include a central opening extendingthrough the upper and lower surfaces, and one or more apertures withinthe intermediate wall segment for receiving a fixation element. The bodymay be configured for insertion along a trajectory represented by anaxis that is oblique relative to a midline of a vertebral body of apatient's spine. The spinal implant may additionally includeanti-migration and/or anti-rotation features as well as visualizationmarkers. The apertures are configured to receive fixation elements, suchas bone screws and the like. The fixation element may comprise one ormore anti-backout features, such as a split ring. The spinal implantfacilitates fusion and may be used with a graft material that can beplaced within the central opening.

In another exemplary embodiment, a method of treating a patient's spinecomprises accessing at least a portion of a patient's spine via anoblique angular approach. A spinal implant is then inserted betweenvertebral bodies of the patient's spine, wherein the spinal implantcomprises a body with an upper surface, a lower surface, and a pair ofsidewalls extending therebetween. The sidewalls may be connected by anintermediate wall segment and converge at a nose or tip. The pair ofsidewalls includes one sidewall that is longer than the other sidewall.The body may further include a central opening extending through theupper and lower surfaces, and one or more apertures within theintermediate wall segment for receiving a fixation element. The spinalimplant is introduced into the patient's spine along a trajectory thatis at an oblique angle relative to the midline of the spine. The spinalimplant may be attached with fixation elements to the vertebral bodies.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the disclosure. Additional features of thedisclosure will be set forth in part in the description which follows ormay be learned by practice of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of thedisclosure and together with the description, serve to explain theprinciples of the disclosure.

FIGS. 1A-1G show perspective views of an exemplary embodiment of aspinal implant of the present disclosure, in which:

FIG. 1A shows a top-down view of the spinal implant;

FIG. 1B shows a perspective isometric view of the spinal implant of FIG.1A;

FIG. 1C shows a perspective oblique view of the spinal implant of FIG.1A;

FIG. 1D shows a rear view of the spinal implant of FIG. 1A;

FIG. 1E shows a side view of the spinal implant of FIG. 1A in use withexemplary bone screws of FIG. 3;

FIG. 1F shows a perspective side view of the spinal implant of FIG. 1Ain use with exemplary fixation screws of FIG. 3; and

FIG. 1G shows a top-down view of the spinal implant and fixation screwsof FIG. 1F.

FIGS. 2A-2B show perspective views of another exemplary embodiment of aspinal implant of the present disclosure, in which:

FIG. 2A illustrates a perspective side view of the spinal implant withexemplary fixation screws of FIG. 3; and

FIG. 2B shows a top-down view of the spinal implant and fixation screwsof FIG. 2A.

FIG. 3 illustrates a perspective view of an exemplary embodiment of abone screw of the present disclosure.

FIG. 4 represents a perspective, top-down view of the spinal implant ofFIG. 1A on a vertebral body.

FIG. 5 illustrates a partial cutaway view of the spinal implant of FIG.1A showing exemplary embodiments of visualization markers of the presentdisclosure.

FIG. 6 illustrates a perspective view of the spinal implant of FIG. 1Ain situ showing exemplary embodiments of visualization markers of thepresent disclosure.

FIG. 7 shows a perspective view of an exemplary embodiment of aninsertion tool of the present disclosure.

FIG. 8 shows the spinal implant of FIG. 1A in use with the insertiontool of FIG. 7.

FIG. 9 represents a perspective view of the spinal implant of FIG. 1A insitu.

DETAILED DESCRIPTION

The present disclosure provides various spinal implants that areconfigured for an oblique angular approach into a patient'sintervertebral disc space. The spinal implant may be introduced througha narrow access window, while maximizing endplate coverage and promotingsagittal balance. The oblique approach may provide better access to morespinal levels, and may be potentially less invasive compared to midlineor lateral approaches.

In accordance with one exemplary embodiment, a spinal implant isprovided having an upper surface, a lower surface, a wall at theanterior portion of the implant, two sidewalls connecting the upper andlower surfaces and converging at a nose or tip near the anterior portionof the implant, and one or more apertures within the posterior portionfor receiving at least one fixation element, wherein the implant isconfigured for insertion at an oblique angle into the patient's lumbarspine. The spinal implant may additionally include anti-migration and/oranti-rotation features, visualization markers and fixation elementguidance features.

Referring now to FIGS. 1A-1G, an exemplary embodiment of a spinalimplant 10 of the present disclosure is shown. The spinal implant 10 maybe configured for insertion at an oblique angle into a patient'sintervertebral disc space. The spinal implant 10 may be employed in thelumbar region of the spine. However, it is contemplated that the spinalimplant 10 may be shaped and sized for use in other areas of the spineas well, such as the thoracic and the cervical region of the spine.Additionally, while the spinal implants 10 of the present disclosure aredescribed as being inserted using an oblique angle approach, it isunderstood that the spinal implants 10 may also be properly insertedusing other techniques as well, including approaches that are notoblique angle approaches. For example, where the shape and geometry ofthe spinal implant 10 is suited for use in a clinical application butthe oblique angle approach is not necessary or desired, then it isunderstood that the spinal implant 10 may be employed, withoutrestriction to the particular surgical technique to insert the spinalimplant 10. In some instances, different spinal levels may require adifferent insertion approach but would still be able to utilize thespinal implants 10 of the present disclosure. Therefore, the spinalimplants 10 may be used at multiple levels, whereby the implants may beinserted at these levels with different approaches.

Turning now to the drawings, according to one exemplary embodiment thespinal implant 10 may include anterior and posterior portions 12, 14,and upper and lower surfaces 16, 18 connected by two sidewalls 20 a, 20b and intermediate wall 22. The two sidewalls 20 a, 20 b may convergeinto a nose or tip 24. This nose or tip 24 may be rounded or tapered.Collectively, the three walls 20 a, 20 b, 22 may together form agenerally triangular profile. However, as shown, one sidewall 20 b maybe greater in length than the other sidewall 20 a, creating a shark'sfin-like shape, as best seen in FIG. 1A. Additionally, the wallscollectively may also form a rounded or approximately rectangular shape,particularly if one or more of the walls is curved or angled itself.

As shown in FIGS. 1C and 1D, the spinal implant 10 may define agenerally wedge shaped or anatomically shaped structure, such as astructure having a sharks fin or arrowhead profile, to more closelymatch the surrounding anatomy of the implant site, for ease of insertion(i.e., to allow tissue distraction), and to be suitable for a tissuesparing or an oblique angular insertion approach. In other words, theheight h₁ of the anterior portion 12 is greater than the height h₂ ofthe posterior portion 14, the upper and lower surfaces 16, 18 extendingalong planes that are angled relative to one another to create thistapered appearance. Exemplary heights may be in the range of about 11,13, and 15 mm, for example. As can be further seen, the implant 10 mayhave rounded edges, particularly along its outer perimeter. Theintermediate wall 22 may extend into convexly curved sidewalls 20 a, 20b that intersect at posterolateral corners 26. The posterolateralcorners 26 may be rounded, as shown, to provide overall smoothness tothe implant profile and prevent undesirable damage to surroundingtissue.

As shown, the spinal implant 10 may include a central opening or lumen30 extending between the upper and lower surfaces 16, 18 to facilitatebony ingrowth or fusion between adjacent bone segments, such asvertebral bodies. If so desired, the opening 30 may be used as a graftcavity to receive and hold bone graft material, or other biologicallyactive materials like bone cement, bone void filler, bone substitutematerial, bone chips, demineralized bone matrix, and other similarmaterials. The spinal implant 10 may be configured in a way thatoptimizes the opening 30 such that the ratio of the cage or implantstructure to the load bearing area is as large as possible. In otherwords, the implant configuration may allow for a relatively largecentral opening 30. As shown in FIG. 1B, a graft containment groove 32may be provided within the opening 30 to contain graft material insidethe graft cavity in the center of the implant 10. This groove 32 may bemachined along the wall of the cavity 30 to provide additional supportin keeping the graft material secured during implantation. Further, thegroove 32 may be convex, such as to serve as a boss extending into thecentral lumen area.

To facilitate attachment of the implant 10 to a tool, such as aninsertion tool or other alignment or rotation instruments, instrumentguides 34 may be provided on the implant 10 to allow specialized toolsto attach to the implant 10. These instrument guides 34, as shown, maybe located at or near the anteriorlateral or posterolateral corners 26.The instrument guides 34 may comprise flat surfaces machined into theimplant 10 as well as shallow grooves or cutout portions. In someembodiments, these instrument guides 34 may be at a 90 degree to theplane of the screw hole. In other embodiments, the instrument guides 34may extend parallel or at an angle to the surgical approach.

The upper and lower surfaces 16, 18 may further include surfaceenhancements 28, such as for example, teeth, ridges, protrusions, ribs,or fins, to enhance bone attachment, prevent migration and generallyprovide more stability. In one embodiment, the anti-migration andanti-rotation features 28 may comprise pyramid-like protrusionsextending from the surface with flattened tops. As further shown, thesefeatures 28 may be grouped or clustered in a specific spatial pattern,such as a diagonal pattern. In some embodiments, the surface features 28may also include a microporous titanium coating on a portion or over theentirety of the features 28. This microporous titanium coating mayadditionally provide resistance to movement and rotation while fixationelements are being applied to the implant. Of course, it is understoodthat alternative surface modifications, such as surface roughenings,barbs, spikes, bumps, etc., may also be employed. Further, biologicalagents, such as bone growth factors may be employed to enhance boneattachment, either alone or in combination with the mechanicalenhancements described above.

The spinal implant 10 may include bore or holes 36 to receive fixationelements such as fixation screws 60 therethrough to secure the spinalimplant 10 to adjacent bone tissue. In the embodiment shown in FIGS.1A-1G, the implant 10 may include three holes 36 for receiving threefixation screws 60. The holes 36 may be configured such that one hole 3is centrally located (i.e., along the center line), and two holes 36 arelaterally located (i.e., beside the center line), as illustrated in FIG.1F. In another embodiment, as shown in FIGS. 2A and 2B, the implant 10may be configured with two holes 36 to receive two fixation screws 60.Between the two holes 36 an inserter instrument engagement opening 42may be provided, as shown in FIG. 2A. Accordingly, the presentdisclosure provides implants 10 having either a three-hole configurationor a two-hole configuration.

In some embodiments, the spinal implant may include other types offixation mechanisms, including for example, blades or keels. Theseadditional fixation mechanisms may be provided in addition to, orinstead of, the fixation elements described above.

FIG. 3 illustrates an exemplary fixation element such as a bone screw 60that may be used with the implants 10 of the present disclosure. Thebone screw 60 may have a head portion 62 and a sharp tip 64 with athreaded shaft 68 extending in between. The sharp tip 64 may comprise asharp knife edge sufficiently sharp to pierce the vertebral bodyendplates, preferably without the need for additional instrumentationsuch as the use of an awl. In one aspect, the screw 60 may becannulated. In one exemplary embodiment, the threaded shaft 68 may be inthe range of about 5.0 mm in diameter, with an inner diameter in therange of about 3.5 mm. The head portion 62 may be a spherically-shaped,shallow screw head having a small radius. The screw head 62 may alsoinclude a tool-engaging opening 72, such as a hex socket, for example.

The bone screw 60 may also be used in combination with an anti-backoutring 74. This ring 74 may comprise a compressible split ring that fitsinto a machined groove 46 in the screw hole 36 to resist screw backout.The bone screw 60 may be provided with an assembled split ring, if sodesired. In addition, the screw 60 may include an optional (not shown)visual marker comprising a groove, band, laser etching, or other similarphysical indicator that disappears from view when the screw is fullyseated, in order to assist with the insertion process. For example,during use, a groove or band laser marked on the screw head 62 otherwiseapparent may disappear from view when the screw 60 is fully seatedwithin the screw hole 36 of the implant 10. Thus, the groove or band onthe screw head 62 would serve as a visual indicator that the screw 60has been properly seated within the hole 36. In some embodiments, thescrews 60 may comprise cancellous bone screws. Of course, other types ofscrews 60 may also be employed. Further, as mentioned above, otherfixation mechanisms such as keels or blades may also be employed forimplant fixation.

According to another aspect of the disclosure, the screws 60 maycomprise a porous coating, such as for example, the screws 60 may beplasma spray coated with titanium powder (CPTi). In one embodiment, thethreaded shaft portion 68 of the screws 60 may have a porous coating orlayer, or may be plasma sprayed. In another embodiment, the screws 60may be coated with a bone growth enhancing material such ashydroxyapatite (HA) on the threaded shaft portion 68. These treatmentsallow for added purchase, and may also assist in torque resistance andreduce the instances of screw spinning within the holes 36. The spinalimplant 10 itself may also be treated, such as for example, the implant10 may contain a porous coating or may be plasma spray coated withtitanium powder (CPTi) on some or all portions of the implant 10, exceptthe screw holes 36 and inserter groove 34. In some embodiments, theporous plasma spray coating may vary in thickness and porosity. Thecoating may be located on some or all portions of the body of the spinalimplant 10, in order to promote ease of insertion and provide an idealsurface for new bone growth onto the surface.

The screw holes 36 may have a loft geometry surrounding it. Meaning,material may be removed around the screw holes 36 to facilitate screwinsertion. Additionally, an indicator groove 46 may be provided on eachof the screw holes 36 to facilitate proper screw seating. This indicatorgroove 46 may be a thin groove that is machined into the screw hole 36so that it is only visible when the screw 60 is fully seated and thesplit ring 74 is engaged, for example. In one embodiment, the screwholes 36 may be configured to remain centered relative to the positionof the implant 10 as the height increases to allow for one introducertool to capture the screw holes 36. In another embodiment, the screwholes 36 may be configured to translate with the endplates during use.Other optional visualization assistance features within the screw hole36 may include etchings, colored bands, or indicator arrows.

Without compromising stability, the lateral holes 36 may be positionedin a manner that avoids the need to retract vessels during surgery.Extended retraction of vessels during surgery may lead to greaterchances for complications to the patient. In the embodiments disclosedherein, the lateral holes 36 are positioned so as to provide easiervisibility of the surrounding implantation site for the surgeon. In theembodiments shown in FIG. 1G and 2B, the screw holes 26 are configuredsuch that the screws 60 converge, whether in the three-screw ortwo-screw configuration. Furthermore, the screw holes 36 may be closelypacked and angled so that the screws 60 converge on the oblique line,which is represented by the line B-B offset from the midline A-A in thethree-screw configuration illustrated in FIG. 4.

As represented in FIG. 1 E, the holes 36 may be configured to allow thescrews 60 to have a horizontal inclination in the range of about 35degrees +/−5 degrees (70 degrees inclusive). Additionally, thepositioning of the holes 36 within the spinal implant 10 enable thescrews 60 to be closely packed or grouped together for easier accessbetween the anterior vessels 4 and psoas muscle 6. With thisconfiguration, it is contemplated that there would be a restriction onthe screw length. Accordingly, in one embodiment the screw lengths mayrange from about 25 to about 30 mm.

The spinal implant 10 may be provided in a variety of sizes, each ofwhich may comprise a distinct footprint size and may be available invarious lodortic angles. As an example, the footprint size of theimplant may be within the range of about 26 mm×38 mm up to about 36mm×48 mm (AP×ML) +/−2 mm. The implant 10 may also be available inlodortic angles of about 8, 12, 14, or 20 degrees, for example. Thesefootprint designs allow the implant 10 to be implanted in the anteriorof the vertebral body off the midline by about 40 degrees, or implantedoff the lateral by about 20 degrees, for instance, and to accommodate amaximum one inch diameter access window on all sizes, as representedFIG. 4 by line W-W. These access window constraints provide access forfixation screw placement through a window in the range up to about a oneinch diameter or 30 mm, while avoiding major vessels 4 and psoas major6, and would require minimal psoas major retraction and thereforeconsidered minimally invasive. Accordingly, in either the two-screwconfiguration or three-screw configuration, the spinal implant 10enables the screws 60 to be positioned within an access window that isno greater than 1 inch in diameter, or 30 mm in width, for minimaldisruption of the adjacent anatomy, due to the grouping of the screwholes 36 closely together. In still other embodiments, however, theimplant 10 may be implanted at an angle off the midline that rangesanywhere from 0 degrees to 180 degrees, resulting in a completelylateral approach.

The spinal implants of the present disclosure may be provided withinternal imaging components to assist in the positioning of the implantsand navigation with the instruments. Due to the off-angle insertionapproach for these implants 10, visualization becomes critical to properplacement within the spine. Accordingly, the implants 10 may alsoutilize anti-rotation visualization cues or radiopaque markers 80 fornavigation, allowing the surgeon determine if the implant is properlyplaced by use of lateral x-rays or intraoperative imaging. These imagingcomponents allow the implants to be easily adjusted, such as byrotating, while within the disc space. The adjustment may be made tocorrect alignment. The imaging components serve as useful navigationtools to otherwise verify proper positioning during the implantationprocess, as well as to check the position of the implant post-surgery.For instance, the visualization markers may be configured for imagingwithin the disc space in specific relation to reference planes oranatomical landmarks to enable adjustments to be made to optimizepositioning of the spinal implant 10 within the disc space.

In some embodiments, the implants 10 may make use of two radiopaquevisualization markers 82, 88. The first marker may comprise ananti-rotation marker 82 that can be used to ensure correct rotationalalignment during the implantation process to promote sagittal balance.This anti-rotation marker 82 may comprise a sphere 84 atop a rod or pin86, as shown in FIG. 5. The rod or pin 86 may be inserted within theimplant 10 via small bores (not shown) located at select positions onthe implant 10. The marker 82 may comprise, in one example, radiopaquetantalum. In another embodiment, the marker 82 may comprise titanium.During visualization via lateral x-rays or intraoperative imaging, ifthe implant 10 is rotated, the top of the marker, or sphere 84, willindicate the direction the surgeon should move the implant to realign.In one contemplated application, the sphere 84 can also be used toindicate facet position. Of course, the markers 82, 84, 86 are notlimited to the shapes or sizes illustrated, and it is understood thatthese markers may comprise any size or geometry such as for example, aring, a sphere, pin or rod, or band, radiopaque coating, a feature, oretching configured to be visualized under radiography.

The second visualization feature may comprise an anti-rotation open ring88. On lateral x-rays or intraoperative imaging, the ring 88 may beobserved as a bright circle. However, if the implant 10 is rotated, anellipse, or no bright spot or “O” shape, will appear under x-rayvisualization or intraoperative imaging. When the implant 10 iscorrectly aligned, the sphere 84 and rod 86 form an “I” image orconstant line, confirming proper rotational position of the implant 10with respect to the C-arm.

These x-ray markers 80 can also be used in A-P (anterior-posterior)x-rays to confirm device position. For instance, as illustrated in FIG.6, the far marker 84, or posterior marker, may be aligned symmetricallyabout the mid-plane. This marker 84 may comprise a sphere, ring, pin,band, radiopaque coating, a feature, or etching, or any other suitableshape or geometry configured to be visualized under radiography.Optionally, a midline marker 92 may be provided to indicate spinousprocess alignment. This midline marker 92, which may be considered ananterior midline marker, may comprise a ring, a sphere, pin or rod,band, radiopaque coating, a feature, or etching, or any other suitableshape or geometry configured to be visualized under radiography.

Alignment verification may be achieved by confirming the position of twoof the radiopaque markers relative to one another, and/or in relation toa central of the midline marker 92. For instance, the markers may bealigned to create a continuous straight line to verify that the spinalimplant 10 is properly aligned. These markers may also be used to adjustor correct the spinal implant position, in order to maximize the segmentangle to be achieved or to achieve a preferred segmental angle oflordosis.

The spinal implant 10 and its components may be formed of any suitablemedical grade material, such as biocompatible metals like stainlesssteel, titanium, titanium alloys, etc. or a medical grade plastic, suchas polyetheretherketone (PEEK) or another radiolucent material, ultrahigh molecular weight polyethylene (UHMWPE), etc. Material stiffnessproperties along with implant geometry are selected to provide aspecific construct stiffness. If so desired, the implant 10 may also beformed of a bioresorbable material. The bioresorbable material may beosteoconductive or osteoinductive, or both.

If desired, the holes 36 of the spinal implant 10 may be configured topermit a predetermined amount of screw toggle (i.e., angular skew) andenable a lag effect when the fixation screw is inserted and residesinside the hole or lumen 36. In other words, the holes 36 may bedesigned to permit a certain degree of nutation by the screw, and thus,the screws may toggle from one position to one or more differentpositions, for instance, during subsidence. It also is believed that thepredetermined screw toggle (permitted by the clearance between thelumen, or hole 36 and the screw) promotes locking of the screw to theimplant 10 after subsidence subsequent to implantation. In oneembodiment, the predetermined amount of screw toggle may be in the rangeof about 3 to 8 degrees, or about 5 to 6 degrees.

Each of the holes 26 may optionally have an opening with a reversechamfer or overhang feature. This overhang feature would enable thesurgeon to better guide the insertion and general approach of thefixation screw 60 into the screw hole 36. Another option may be toprovide the openings 36 with a countersink. The countersink feature'scenter may be offset to the center axis of the hole 36, allowing acountervailing force when the surgeon applies pressure on the fixationscrew 60 during insertion, and providing a tactile feedback response tolet the surgeon know when the fixation screw's head 62 is properlyseated. Thus, the offset would cause the screw head 62 to become loaded(i.e., provide feedback) on final positioning. A portion of thecountersink 40 may further optionally have a spherical surfaceconfigured to provide a visual feedback response to the surgeon. Ofcourse, the quality and strength of the feedback response also dependson the quality of the bone tissue at the area of treatment. Healthynormal bone tissue will obviously provide the best feedback, asunhealthy, diseased or damaged bone tissue would not have sufficientstrength to provide the necessary countervailing force.

FIG. 7 represents an exemplary embodiment of an inserter instrument 100that can be used with the spinal implants 10 of the present disclosure.Inserter instrument 100 may comprise an elongate shaft 102 having spacedapart cleaning slots 106 along its length. The elongate shaft 102 mayterminate in a back plate 118 at the working end 110 of the instrument100. The back plate 118 may be configured to rest against the spinalimplant 10, while side bars 112 extending from the back plate 118 may beprovided to slide into and securely fit within the instrument guides 34along the sides of the implant 10. A centrally located insertion pin 114may be provided to grasp the middle or central screw hole 36 of thethree-hole configured implant 10 (see FIG. 8), or the inserterinstrument engagement opening 42 in the two-hole configured implant 10.This centrally located insertion pin 114 may cooperate with an actuatingshaft 136 housed inside the elongate shaft 102. In some embodiments,this pin 114 may be threaded for engagement with a threaded opening onthe implant 10.

As shown, the elongate shaft 102 may be attached to a handle 120 at aneck region 122 of the handle 120. The handle may include a grippingportion 124, and cleaning slots 126. In addition, the handle 120 mayinclude an actuating mechanism 130 to operate the actuating shaft 136.In one embodiment, the actuating mechanism 130 may include a rotatingknob 136 that, when rotated, results in the movement of the actuatingshaft 136 and consequent translation of the insertion pin 114. In use,the rotating knob 136 may be rotated to allow the insertion pin 114 toengage the middle screw hole 36 of the spinal implant 10 (of thethree-hole configuration), as shown in FIG. 8, or the inserterinstrument engagement opening 42 of the spinal implant 10 (of thetwo-hole configuration). When the implant 10 has been properly inserted,the inserter instrument 100 may easily be removed by de-rotating theactuation knob 136, releasing the middle insertion pin 114 from thescrew hole 36 or inserter instrument engagement opening 42, and slidingthe side bars 112 away from the instrument guides 34.

In one exemplary method of inserting the spinal implant 10, anapproximately 40 degree from the midline approach is used with thepatient in a supine position. In another exemplary method, anapproximately 50 degree from the lateral approach is used with thepatient in the lateral position. These two approaches reduce contactwith psoas 6 and vessels 4. Accordingly, what is meant by an obliqueangular approach is an insertion trajectory along an axis represented bythe line B-B that is angularly offset from the midline represented bythe line A-A by angle α, as represented in FIG. 4, with line A-Prepresenting the anterior-posterior direction, line M-L representing themedial-lateral direction, and line F-F representing the distance betweenfacets.

First, in order to set the approach angle, A-P and lateral x-rays may betaken of the spine. From the vertical axis, under fluoroscopy, the C-armmay be rotated by the appropriate degree (i.e., 40 or 50 degrees) basedon the type of approach taken, as previously mentioned. Of course, theC-arm may also be rotated by other angles, such as for example, from arange of 0 degrees off the midline to about 90 degrees from the midline.

Next, an incision may be created and the user may approach the spine inline with the previously determined C-arm angle from the prior step, viaa retroperitoneal approach. A dilator may be used to confirm disclocation, with a bias to the psoas, and a K-wire may be placed throughthe dilator. The dilator can then be replaced with a slide instrument.Retractor blades can then be inserted to retract psoas 6 to create anaccess window approximately 30 mm wide, or about 1 inches in diameter,or smaller. Vasculature should be avoided during the process.

Then, the surgeon may prepare the implantation site by removing somedisc material from the disc space (i.e., diskecktomy) using availableinstrumentation. The spinal implant 10 may be provided to the surgeonwith the screws pre-attached, or separately, as desired. Once theimplant 10 is loaded onto an inserter instrument 100, such as the oneshown in FIG. 7, the implant 10 may be aligned with the center screwhole 36 angled superiorly. The surgeon then introduces the implant 10under fluoroscopy.

Following insertion, the surgeon visualizes and verifies proper implantpositioning. If the sphere marker 84 of the implant 10 is posterior, thesurgeon would move the inserter instrument 100 posterior or closer tothe C-arm of the fluoroscope so the marker 86 and sphere marker 84 forma single constant line (or close to it) . If the sphere marker 84 isanterior, then the surgeon would move the inserter instrument 100anterior or away from the C-arm.

Starting with the center screw hole 36, the surgeon can now insert thebone screw 60 into the center hole 36 first, in a three-screwconfiguration, and then follow with insertion of the other bone screws60 in the other holes 36 lateral to the center hole. Finally, A-P andlateral x-rays may be taken to confirm the final implant position. Screwinsertion may be accomplished via a very narrow access, with an accesswindow no greater than about 30 mm or 1 inch in diameter as mentionedabove, for a three-screw configuration (the window could be even smallerfor a two-screw configuration). Accordingly, this entire process may beaccomplished as an open or a minimally invasive procedure, maximizingendplate coverage and promoting sagittal balance. The oblique approachdescribed herein provides better access to more spinal levels and ispotentially less invasive than midline or lateral approaches. Asillustrated in FIG. 9, in situ, the spinal implant 10 may be fullyinserted while avoiding any disruption of the anterior vessels 4 orpsoas major 6 during insertion by this approach.

Where toggling is desired, the implant 10 may be configured to permit apredetermined amount of screw toggle and enable a lag effect when thefixation screw is inserted and resides inside the screw hole 36. Upontightening, the lag effect may be observed whereby the implant 10 drawsbone tissue towards itself, which may promote better fusion. Since thescrews do not completely lock due to the lag effect, no screw backoutoccurs.

It will also be appreciated that the angular positioning of the variousholes, as described above, allows the present implant 10 to be of arelatively small size and therefore insertable from an oblique angularapproach into the intervertebral spaces of the spine. Thus, it will beappreciated that the angular positioning of the holes can assisteffective operation of the implant 10 and the ability to “stack”implants in adjacent multilevel procedures without the securing meansinterfering with each other. Such a feature can be of major significancein some situations and applications.

Although the following discussion focuses on spinal implants orprostheses, it will be appreciated that many of the principles mayequally be applied to other structural body parts within a human oranimal body.

Other embodiments of the disclosure will be apparent to those skilled inthe art from consideration of the specification and practice of thedisclosure provided herein. It is intended that the specification andexamples be considered as exemplary only.

What is claimed is:
 1. A spinal implant comprising: a body having anupper surface, a lower surface, and a pair of sidewalls extendingtherebetween, the sidewalls being connected by an intermediate wallsegment and converging at a rounded nose, the pair of sidewallsincluding one sidewall that is longer than the other sidewall, the bodyfurther including a central opening extending through the upper andlower surfaces, and one or more apertures within the intermediate wallsegment for receiving a fixation element; wherein the body is configuredfor insertion along a trajectory represented by an axis that is obliquerelative to a midline of a vertebral body of a patient's spine.
 2. Thespinal implant of claim 1, wherein the upper and lower surfaces extendalong planes that are angled relative to one another to form a generallywedgeshaped or anatomically shaped profile for the body.
 3. The spinalimplant of claim 1, wherein the sidewalls intersect the intermediatewall segment at rounded posterolateral corners.
 4. The spinal implant ofclaim 1, wherein the spinal implant has rounded outer edges.
 5. Thespinal implant of claim 1, wherein the implant includes visualizationmarkers.
 6. The spinal implant of claim 5, wherein the visualizationmarkers are configured for imaging within the disc space in relation toreference planes or anatomical landmarks.
 7. The spinal implant of claim6, wherein the visualization markers comprise a sphere, rod, ring, band,radiopaque coating, a feature, or etching configured to be visualizedunder radiography.
 8. The spinal implant of claim 1, wherein theapertures are configured to allow the fixation elements to converge onthe oblique angular trajectory axis of the insertion approach.
 9. Thespinal implant of claim 1, wherein the apertures are configured for anarrow access window of approximately a one inch diameter or less. 10.The spinal implant of claim 1, wherein there are at least two apertureson the body of the spinal implant.
 11. The spinal implant of claim 1,wherein the body further includes instrument guides along the sidewalls.12. The spinal implant of claim 1, wherein the body includes a graftcontainment groove surrounding the central opening.
 13. The spinalimplant of claim 1, wherein the body further includes anti-migrationfeatures.
 14. The spinal implant of claim 13, wherein the anti-migrationfeatures are also anti-rotation features.
 15. The spinal implant ofclaim 13, wherein the anti-migration features comprise pyramid-shapedprotrusions having flat top surfaces.
 16. The spinal implant of claim15, wherein the protrusions are grouped in a diagonal pattern.
 17. Thespinal implant of claim 1, further including a porous coating on aportion of the body.
 18. The spinal implant of claim 17, wherein theporous coating comprises a plasma sprayed coating.
 19. The spinalimplant of claim 18, wherein the plasma spray coating has varyingthickness and porosity.
 20. The spinal implant of claim 1, wherein thefixation element comprises a bone screw.
 21. A method of treating apatient's spine, comprising: accessing at least a portion of a patient'sspine; inserting a spinal implant between vertebral bodies of thepatient's spine, wherein the spinal implant comprises: a body having anupper surface, a lower surface, and a pair of sidewalls extendingtherebetween, the sidewalls being connected by an intermediate wallsegment and converging at a rounded nose, the pair of sidewallsincluding one sidewall that is longer than the other sidewall, the bodyfurther including a central opening extending through the upper andlower surfaces, and two or more apertures within the intermediate wallsegment for receiving a fixation element; wherein the spinal implant isintroduced into the patient's spine along an axis of trajectory that isat an oblique angle relative to the midline of the spine.
 22. The methodof claim 21, wherein the spinal implant includes visualization markers,and further including the step of positioning the implant by observingthe visualization markers under x-ray or intraoperative imaging.
 23. Themethod of claim 22, wherein at least one of the visualization markers isa radiopaque anti-rotation marker, and further including the step ofverifying alignment of the spinal implant by confirming the correctposition of two of the visualization markers relative to one another.24. The method of claim 23, wherein the step of verifying alignment ofthe spinal implant comprises aligning two visualization markers tocreate a continuous straight line.
 25. The method of claim 21, whereinthe spinal implant includes visualization markers, and further includingthe step of adjusting the implant position by observing thevisualization markers until a maximum segment angle is achieved.
 26. Themethod of claim 21, wherein the spinal implant includes visualizationmarkers, and further including the step of adjusting the implantposition by observing the visualization markers until a preferredsegmental angle of lordosis is achieved.
 27. The method of claim 23,further including the step of securing the spinal implant with fixationelements after proper implant position has been verified.